Convergent evolution of parrotfish beaks enables stress redistribution during high-force feeding

Convergent evolution is often interpreted as evidence that similar ecological challenges select for optimal functional solutions, yet the biomechanical mechanisms underlying such convergence remain poorly resolved. Parrotfishes independently evolved fused, beak-like dentition multiple times, a trait associated with feeding on hard substrates such as coral, but its advantage has not been quantified. Here, we combine finite element analysis with shockwave modeling to evaluate the performance of the beak during feeding. Across five species spanning independent evolutionary origins of beaked and non-beaked dentitions, we find that jaw opening is governed primarily by geometric scaling, with minimal influence from dentition morphology. In contrast, under stabilized biting, fused dentition reduces the rate of stress accumulation relative to discrete teeth, indicating a functional advantage under constrained loading. Shockwave modeling further shows that tooth geometry and stacking regulate stress propagation: smooth profiles reduce stress concentration, while stacked architectures localize stresses within the tooth material and limit transmission into the surrounding bone. These results suggest that convergent beak evolution in parrotfish reflects repeated optimization for stress management under constrained and impact loading, and reveals a general principle by which biological structures control internal force transmission during high-force feeding rather than maximize strength alone.